Personal care absorbent articles such as diapers, training pants, incontinence devices, feminine hygiene products, and the like are designed to absorb body liquids including blood, urine, menses and feces. In certain instances, these products should be able to quickly absorb relatively large quantities of liquid, urine being an example, and still keep the wearer as dry and comfortable as possible. Typically, such personal care absorbent products include a liquid permeable top sheet, a bottom sheet, and an absorbent core disposed between the top sheet and the bottom sheet. The top sheet is usually made from some type of fibrous permeable nonwoven web such as a bonded carded web or a spunbond web. The bottom sheet typically is made from some type of material or laminate which is liquid impervious, and optionally, breathable.
The absorbent core is usually made from wood pulp fibers also referred to as “fluff” and can optionally include superabsorbent particles which are designed to absorb many times their own weight in liquid. When a child or adult urinates, the urine passes through the top sheet and is absorbed into the absorbent core below. A problem with the absorbent cores is that they are not very effective at quickly channeling liquid away to more remote parts of the absorbent structure. As a result, at least a part of the liquid retained in the core may wick back to the top sheet which is usually in contact with the wearer's skin. This urine-soaked material is at the very least uncomfortable, inhibits air flow to the skin and may possibly exacerbate any skin conditions which are present. Further, liquid not contained by the absorbent core or liquid management layer presents a higher risk of leakage outside the personal care absorbent article.
Attempts have been made to alleviate these problems by placing one or more additional layers of materials between the top sheet and the absorbent core. These materials have been referred to as a liquid management layer, transfer layer, separator layer, surge layer, fluid acquisition and distribution layer, as well as other names (collectively referred to as “liquid management layer”). The function of the liquid management layer is to take up the liquid delivered to it through the top sheet and then transfer the liquid to the absorbent core. Ideally, such a liquid management layer would readily take in liquid to get it away from the skin. The liquid management layer would give up the same liquid to other components in the personal care absorbent product and would be able to separate the skin and top sheet from the rest of the absorbent system. Lastly, the liquid management layer would be able to maintain the separation under a variety of conditions.
Current liquid management layers are able to receive considerable amounts of liquids, move the liquids away from the skin of the wearer, distribute the liquid through and across the liquid management layer, and transfer the liquid to the absorbent core. Typical liquid management layers utilize high loft materials exhibiting high void volumes. For example, U.S. Pat. No. 5,846,166 to Bishop, et al. describes a surge layer for a personal care absorbent article where the material has a void volume ranging from about 80 cc/g to about 117 cc/g. Similarly U.S. Pat. No. 5,490,846 to Ellis, et al. describes a material with a void volume ranging from 40 cc/g to about 60 cc/g. The trend has been to use high loft materials with high void volumes to provide a large space for liquid to be stored temporarily as the liquid is transferred and absorbed by the absorbent core. Often these materials utilize crimped fibers to increase loft and void volumes of the materials. For example, U.S. Pat. No. 6,096,015 to Yeo, et al. discloses a material for a separator layer with fibers of at least 28 microns and discloses that the fibers of the separator layer have a minimum of five crimps per extended inch. While, Yeo, et al. discloses two comparative examples which utilize uncrimped fibers; however, these materials appear to have void volumes greater than 25 cc/g.
One challenge with the high loft materials is compressibility. When the high loft material is placed under load either by the weight of the wearer or in storage, the pore structure of the material changes due to its compressibility. As the pore structure changes under load, the performance of the material changes. Some have used a mixture of relatively large fiber sizes and small fiber sizes to reduce compressibility of the liquid management layer. For example, U.S. Pat. No. 5,364,382 to Latimer, et al. describes using larger, stiffer fibers to provide resiliency and using smaller fibers to increase the available surface area in the material. These types of materials typically have a large number of high loft compressible fibers and exhibit high void volumes. Another liquid management layer is disclosed in U.S. Pat. No. 5,522,810 to Allen, Jr., et al. which describes a compressively resistant and resilient fibrous nonwoven web for use as a liquid management layer that is at least 2.5 mm thick. While this material is compressively resistant, it adds to the overall bulk of the personal care absorbent article.
Another issue with high void volume liquid management layers is the volume they occupy while in bulk form on a roll during storage or transportation prior to being assembled as part of a personal care absorbent article. This is because these high loft materials have a tendency to collapse in a non-reversible way when wound on the roll if the winding tension is too high. Further, in view of using a relatively low winding tension and the thickness of these high loft materials, for rolls of equal diameters, the roll of high void volume liquid management material can have a shorter length of material per roll than a roll of a thinner material. These shorter rolls lead to more frequent roll changes, more waste, and more frequent material splices during the manufacturing process which, in turn, cause delays in production of the personal care absorbent articles.
There is a need for a resistant and resilient liquid management layer which is thinner than that currently realized, which does not add to the bulk of the personal care absorbent article, and yet provides adequate separation between the absorbent core and the top sheet against the surface of the wearer upon multiple insults. Further, there remains a need in the absorbent personal hygiene field for a liquid management layer that maintains its pore structure while under load and can be produced relatively economically compared to carded materials, while still providing necessary performance features for use as a liquid management layer. Many of the materials discussed above are high loft compressible materials or they are thick resilient materials. A proposed solution might be to simply make the materials thinner. Simply making a material thinner can have significant adverse effects upon performance. Therefore, unique properties must be combined to provide a thinner, compression resistant liquid management layer that still meets the performance requirements for a liquid management layer in a personal care absorbent article. The present invention is directed to such a liquid management layer as will become more apparent from the following description, drawing, and claims.